This application claims the priority of German Patent Application Serial No. 101 53 750.6, filed Oct. 31, 2001, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference.
The present invention relates to a rotor for an electric machine, in particular a permanent magnet (PM) synchronous machine. More particularly, the present invention relates to a punched sheet metal unit for electrical machines with a substantially ring-shaped punched metal plate, which has its center an opening for receiving a shaft, and a plurality of recesses arranged along the periphery of the metal plate, wherein one or more corresponding permanent magnets can be inserted in the recesses.
The permanent magnets in a rotor of asynchronous machines excited with permanent magnets are embedded radially in the rotor iron. The permanent magnets can be arranged in a flux concentration arrangement and magnetized alternatingly with different tangential magnetization directions. A rotor of this type is described in EP 0 803 962 A1. The punched sheet metal packet of the rotor described therein has an opening for receiving a holding element in the form of a hollow cylinder. This holding element secures the permanent magnets in the gaps of the sheet metal packet and should be made of a non-magnetic material to avoid stray flux. The sheet metal packet is held with screws between two coupling flanges to ensure its stability. The bolts and/or screws extend through both coupling flanges as well as through the sheet metal packet.
Rotors with permanent magnets implemented in a flux-concentrating design have a fundamental problem in that stray flux "PHgr"s can propagate through the shaft. The stray flux "PHgr"s can be reduced by employing non-magnetic materials, air gaps or easily saturable, thin soft-magnetic junction elements between the permanent magnet and the shaft. However, such arrangements disadvantageously either use expensive materials and have a complex design, or still exhibit a residual, potentially significant stray flux.
It would therefore be desirable and advantageous to provide an improved rotor for a permanent magnet synchronous machine to obviate prior art shortcomings and to minimize the stray flux transmitted through the shaft while retaining a simple design of the sheet metal packet.
According to one aspect of the invention, a punched sheet metal unit for electrical machines with a substantially ring-shaped punched metal plate has in its center an opening for receiving a shaft, and a plurality of recesses arranged in the circumferential direction, wherein at least two permanent magnets can be inserted in each of the recesses. A corresponding intermediate sheet metal segment is arranged or can be arranged in each of the recesses between the permanent magnets. At least one of the recesses is shaped so as to form an air gap between the surface of the intermediate sheet metal segment that is oriented radially inwardly towards the center and an edge of the recess that is oriented radially outwardly from the center, when the permanent magnets are inserted radially towards the outside.
According to another aspect of the invention, a punched sheet metal module includes a plurality of connected punched sheet metal units sequentially arranged in an axial direction, with the punched sheet metal units including a substantially ring-shaped punched metal plate having a central opening adapted to receive a shaft, a plurality of recesses formed in the metal plate and arranged in a circumferential direction of the metal plate, each of said recesses adapted to receive at least two permanent magnets, and an intermediate sheet metal segment arranged between the at least two permanent magnets. The intermediate sheet metal segment has a peripheral edge and an inward edge facing the opening, wherein an air gap is formed between the inward edge of the intermediate sheet metal segment and an edge of the recess proximate to the opening when the at least two permanent magnets are inserted in such a way as to contact the respective recesses.
Embodiments of the invention may include one or more of the following features. The air gap in at least one of the recesses can abut surfaces of the at least two permanent magnets that are oriented towards the opening. The intermediate sheet metal segments can be connected in a peripheral region of the punched sheet metal and also formed as one piece with the punched sheet metal. Additionally employed separation sheet metal segments which can be formed as one piece with the punched sheet metal can be provided to separate the recesses from each other. The separation sheet metal segments can be connected with adjacent intermediate sheet metal segments in a peripheral region of the punched metal plate.
Advantageously, at least one of the recesses can be open at a peripheral edge of the metal plate and at least one of the separation sheet metal segments can have at least one tangentially arranged nose formed proximate to the peripheral edge of the metal plate, wherein the nose can hold at least one of the permanent magnets disposed in a recess. The permanent magnets can also be held in place by providing the intermediate sheet metal segments on their inward edges with tangentially formed noses. Alternatively, to prevent the intermediate sheet metal segments and/or the permanent magnets from being ejected by the centrifugal force, at least one holding element can be disposed in a corresponding recess and configured to hold the at least two permanent magnets in the recess in a predetermined position. The holding element can be secured by providing mounting recesses in the inward edge of the intermediate sheet metal segment and in the edge of the recess proximate to the opening, wherein the mounting recesses can engage with the holding element. To minimize the stray flux, the holding element can be made of a non-magnetic material, such as aluminum, an aluminum alloy, brass, non-magnetic stainless steel and plastics.
The punched sheet metal units of the punched sheet metal module can be connected with each other by one or more bolts extending through the punched sheet metal units, an/or by impregnating, potting and/or gluing.